Not applicable.
The present invention relates to ink jet printing and in particular discloses a shape memory alloy ink jet printer.
The present invention further relates to the field of drop on demand ink jet printing.
Many different types of printing have been invented, a large number of which are presently in use. The known forms of print have a variety of methods for marking the print media with a relevant marking media. Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and inkjet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.
In recent years, the field of ink jet printing, wherein each individual pixel of ink is derived from one or more ink nozzles has become increasingly popular primarily due to its inexpensive and versatile nature.
Many different techniques on inkjet printing have been invented. For a survey of the field, reference is made to an article by J Moore, xe2x80x9cNon-Impact Printing: Introduction and Historical Perspectivexe2x80x9d, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).
Ink Jet printers themselves come in many different types. The utilisation of a continuous stream ink in ink jet printing appears to date back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electro-static ink jet printing.
U.S. Pat. No. 3,596,275 by Sweet also discloses a process of a continuous inkjet printing including the step wherein the ink jet stream is modulated by a high frequency electro-static field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex (see also U.S. Pat. No. 3,373,437 by Sweet et al).
Piezoelectric inkjet printers are also one form of commonly utilized inkjet printing device. Piezoelectric systems are disclosed by Kyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) which discloses a squeeze mode of operation of a piezoelectric crystal, Stemme in U.S. Pat. No. 3,747,120 (1972) discloses a bend mode of piezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 discloses a piezoelectric push mode actuation of the ink jet stream and Fischbeck in U.S. Pat. No. 4,584,590 which discloses a shear mode type of piezoelectric transducer element.
Recently, thermal ink jet printing has become an extremely popular form of ink jet printing. The ink jet printing techniques include those disclosed by Endo et al in GB 2007162 (1979) and Vaught et al in U.S. Pat. No. 4,490,728. Both the aforementioned references disclosed ink jet printing techniques rely upon the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture connected to the confined space onto a relevant print media. Manufacturers such as Canon and Hewlett Packard manufacture printing devices utilizing the electro-thermal actuator.
As can be seen from the foregoing, many different types of printing technologies are available. Ideally, a printing technology should have a number of desirable attributes. These include inexpensive construction and operation, high-speed operation, safe and continuous long-term operation etc. Each technology may have its own advantages and disadvantages in the areas of cost, speed, quality, reliability, power usage, simplicity of construction operation, durability and consumables.
It is an object of the present invention to provide for a new form of ink jet printing device that utilizes a shape memory alloy in its activation method.
According to the invention, there is provided a method of fabricating a fluid-ejecting chip for an inkjet printer, the method comprising the steps of:
forming CMOS layers on a wafer substrate;
forming nozzle chamber walls on the wafer substrate to define a plurality of nozzle chambers on the substrate with an ink ejection port in fluid communication with each nozzle chamber;
depositing a sacrificial material on the wafer substrate;
depositing a shape memory material on the sacrificial material at a temperature above a transition temperature of the shape memory material so that the shape memory material is in a post-actuation shape;
forming heating circuits on the sacrificial material to be in electrical contact with the CMOS layers and to heat the shape memory material upon receipt of an electrical signal from the CMOS layers to a temperature above the transition temperature;
depositing a stressed material on the sacrificial material; and
removing the sacrificial material so that the shape memory material and the stressed material define a plurality of actuators that are operatively arranged with respect to the nozzle chambers and the stressed material deforms the actuators into a pre-actuation condition at a temperature below the transition temperature, so that, when heated, the shape memory material returns to the post-actuation shape, and the resultant movement of the actuators having the heated shape memory material causes the fluid to be ejected from the corresponding fluid ejection ports.
The method may include the steps of:
depositing a layer of etch stop material on a discharge side of the substrate;
etching the substrate from an inlet side of the wafer up to the etch stop layer to define each nozzle chamber, so that etched sides of the substrate define the nozzle chamber walls;
etching the etch stop layer to define each ink ejection port; and
filling each nozzle chamber with the sacrificial material prior to depositing the shape memory material and forming the heating circuits.
The method may include the steps of:
depositing a first layer of a stressed material on the sacrificial material;
depositing a layer of a shape memory alloy on the first layer of stressed material so that the layer of the shape memory alloy is in electrical contact with the CMOS layers;
etching the shape memory alloy to define the heating circuits; and
depositing a second layer of a stressed material on the sacrificial material so that each heating circuit is positioned between the layers of stressed material.
The actuator thus comprises a conductive shape memory alloy panel in a quiescent state and which transfers to an ink ejection state upon heating thereby causing said ink ejection from the chamber. Preferably, the heating occurs by means of passing a current through the shape memory alloy. The chamber is formed from a crystallographic etch of a silicon wafer so as to have one surface of the chamber substantially formed by the actuator. Advantageously, the actuator is formed from a conductive shape memory alloy arranged in a serpentine form and is attached to one wall of the chamber opposite a nozzle port from which ink is ejected. Further, the nozzle port is formed by the back etching of a silicon wafer to the epitaxial layer and etching a nozzle porthole in the epitaxial layer. The crystallographic etch includes providing sidewall slots of non-etched layers of a processed silicon wafer so as to extend the dimensions of the chamber as a result of the crystallographic etch process. Preferably, the shape memory alloy comprises nickel titanium alloy.